In the manufacture of products wherein a desired material, such as a beverage, is marketed in a sealed container, it is necessary at some stage of the manufacturing operations to provide lids to be secured on the containers. The lids are put through a required number of operations to place them in condition to be applied to the containers. One of these operations relates to the curling back of the outer portions of the lid leaving a surface to be contacted by the open end of a filled container. In many instances, this surface, including a portion of the curled portion, is provided with a coating of a sealant material. One quality control operation is to determine the inner and outer radial extent of the coating and whether too much or too little of the coating has been applied to a lid. Another quality control operation is to determine what the outer circumference of the lid was, before the curling operation, whether or not a coating of the sealant has been applied thereto. One prior art procedure known to the applicant involves the use of a tool, similar to a bottle cap opener, to peel back successive increments of the curled back portion of the container lid in a repeated series of operations. While this does provide some basis for quality control it is time consuming and not very accurate.